An end carboxyl bearing reactive vinyl monomer exemplified by acrylic acid, methacrylic acid and the like has been well known as a constituting unit of an acrylic resin. Such monomer is usually copolymerized with other acrylic monomers as acrylates, methacrylates and the like to improve the adhesion properties of the resulting resin to a metal substrate or to improve the curing properties of the resin to be compounded with an aminoplast resin.
However, in the heretofore proposed end carboxyl bearing vinyl monomers, the chain length between the vinyl group and the carboxyl group is relatively short and therefore, even when incorporated into a vinyl resin, the curing acceleration effect is not so good and the adhesion improvement is rather poor. Thus, the actual use of these monomers has been limited in certain cases.
Therefore, there is a strong demand for a novel class of end carboxyl bearing reactive vinyl monomers, which will exert, when incorporated into a vinyl resin, a strong catalytic action in a crosslinking reaction of the resulting resin with an aminoplast resin, and capable of improving the adhesion properties of the vinyl resin to metal substrates. In answer to these demands, the inventors have previously proposed a novel class of end carboxyl bearing reactive vinyl monomers of the formula: ##STR2## wherein R.sub.1 is hydrogen or methyl group; R.sub.2 is a substituted or unsubstituted aliphatic hydrocarbon having 2 to 10 carbon atoms, an alicyclic hydrocarbon having 6 to 7 carbon atoms or an aromatic hydrocarbon having 6 carbon atoms; D is a repeating unit of ##STR3## R.sub.4 is ethylene or propylene; R.sub.5 is a substituted or unsubstituted alkylene having 2 to 7 carbon atoms; R.sub.6 is a substituted or unsubstituted alkylene having 2 to 5 carbon atoms; m is an integer of 1 to 10 and n is an integer of 2 to 50. (Japanese Patent Application No. 1899/86, publicly opened as 161742/87 on July 17, 1987).
In these kinds of reactive vinyl monomers, since a long chain of alkylene group is present between the reactive vinyl group and the end carboxyl group, said monomer can provide, when incorporated into a resin, a highly active carboxyl group at the end portion of pendant group of the resin and such carboyl group can afford a strong catalytic action in the crosslinking of the resin with an aminoplast resin.
Thus, the crosslinking rate is greatly improved and a highly gellated coating can be obtained.
Furthermore, in that monomer, there is included both a hydrophilic portion represented by the end carboxyl group and a hydrophobic portion represented by the alkylene chains of R.sub.2 and D and the ratio of these portions may be freely controlled as desired. The presence of such hydrophilic and hydrophobic portions in the same structure of the monomer compound will exert a strong surface activation power.
Therefore, when the reactive vinyl monomer is used in a neutralized and solubilized form, an emulsion or dispersion polymerization of .alpha., .beta.-ethylenically unsaturated compounds can be effected without using an external emulsifier, thereby obtaining a resinous emulsion capable of resulting in a coating with excellent water resistance and other desired properties.
However, in the actual coatings technology, an appropriate amount of various organic solvents including cellosolves, such as ethyl cellosolve, butyl cellosolve and the like, alcohols, such as ethanol, isopropanol, butanol and the like, esters, such as ethyl acetate, butyl acetate and the like, aliphatic hydrocarbons, such as hexane, heptane and the like, and aromatic hydrocarbons, such as benzene, toluene, xylene and the like are often added to a coating composition based on such resinous emulsion, for the object of controlling the solvent evaporation rate or in the composition's viscosity.
At that time, the resin particles contained therein should be still maintained in a stabilized form of a dispersion, otherwise the coating appearance will be adversely affected therewith. Recently, various attempts have been made to first prepare vinyl resin emulsion through an emulsion polymerization and then replace water with an organic solvent to obtain an organic solvent dispersion of vinyl resin particles, which is to be used in a solvent type coating composition.
Therefore, the resin particles thus formed should be well adapted both in respect to the aqueous coating composition and in the solvent type coating composition.
The aforesaid reactive vinyl monomers of Japanese Patent Application No. 1899/86 (Kokai No. 161742/87) are indeed excellent in both respect to the catalytic action in the crosslinking of a vinyl resin with an aminoplast resin and in the interfacial activity required for an emulsifier, but are not sufficient in respect to amphiphatic properties and especially hydrophobic properties which is believed to be essential in the aforementioned latest demands.
One promising clue for the improvement in clarity, and water resistance of a coating made of a resinous emulsion and film-forming property thereof is to control the resin particle diameter in the emulsion at will and to provide as fine particles as possible. To this end, it is highly desirable to increase the hydrophobic nature of the said reactive vinyl monomer to be used as an internal emulsifier, without destroying the good balance of hydrophilic and hydrophobic properties thereof, thereby improving the solubility towards oily substances as polymerization monomers and the like and having a stable dispersion of the finest particles of polymerization monomers in an aqueous medium.
It is, therefore, an object of the invention to provide a reactive vinyl monomer having not only the desired properties of an internal emulsifier and a crosslinking catalyst, but also the characteristic features of increased amphiphatic properties and especially improved solubility towards oily substances as polymerization monomers and organic solvents, which is specifically useful in an emulsion polymerization of .alpha., .beta.-ethylenically unsaturated compounds without using any external emulsifiers to give a stable dispersion of fine vinyl resin particles.
An additional object of the invention is to provide an economically advantageous method for the preparation of such vinyl monomers.
Other objects of the invention are to provide vinyl resin particles from said reactive vinyl monomers, which are applicable to both aqueous paint and solvent type coating compositions, to provide an economically advantageous method for the preparation of said resin particles, and to provide a stable aqueous or organic solvent dispersion of such resin particles, which is specifically useful in various technical fields including paint, ink and plastic industies.